A. Field of the Invention
This invention relates to the field of data communication and data-over-cable systems. More particularly, the invention relates to a method of graphically representing conditions in such a system (such as signal to noise ratio, noise floor levels, or other types of conditions, which may or may not indicate an impairment in the system) in a convenient manner such that the source of the impairment to the system is easy to comprehend by a technician or human operator.
B. Description of Related Art
Cable modem systems for wide area network access, e.g., Internet access, are now being rolled out in selected metropolitan areas of the United States. Basically, these systems provide high-speed data communications over a cable television infrastructure. Background information related to cable modem systems in general is described in the Data-Over-Cable Service Interface Specifications (DOCSIS)xe2x80x94Radio Frequency Interface Specifications, Interim Draft, dated Jul. 24, 1998, issued by Cable Television Laboratories, Inc. This document, known to persons working in the art, is incorporated by reference herein in its entirety.
The basic overall architecture of a data over cable system is shown in FIG. 1. The system of FIG. 1 provides a mechanism by which a computer 10 connected to a backbone network 12 (either directly or indirectly by intermediate networks) may communicate with another computer 14 via a cable television infrastructure indicated generally by reference numeral 16. The cable television infrastructure 16 includes a distribution hub or xe2x80x9chead-endxe2x80x9d 18 that is connected to the backbone network 12 via a wide area network and a switch or router 20. A cable system head-end is a central location in the cable television network that is responsible for sending cable signals in the downstream direction. The head-end 18 modulates digital data into analog form and supplies analog signals to a fiber network 22, which is connected to a plurality of O/E nodes 24. The O/E nodes 24 convert optical signals in the fiber network 22 to electrical signals for transmission over a coax cable network 26 to a cable modem 28 at the customer""s location. The cable modem 28 demodulates the analog signals and extracts the digital data and supplies the data to the customer promises equipment 14, which, in a typical situation, is a general purpose computer in a home environment.
The head-end 18 includes a cable modem termination system or CMTS 30. This device provides a network side interface to a wide area network, indicated at 32, and an RF interface between the cable modem termination system and the cable network in both the downstream and upstream directions, indicated at 34 and 36. The term xe2x80x9cdownstreamxe2x80x9d, as used in the present document, refers to transmission in the direction from the head-end 18 or cable modem termination system 30 to the cable modem 28 at the customer premises. The term xe2x80x9cupstreamxe2x80x9d refers to transmission in the direction from the cable modem 28 at the customer premises to the cable modem termination system 30.
For transmission in the downstream direction, the CMTS 30 supplies data from the computer 10 to a modulation circuit MOD and to a combiner 38, where the data is combined with video signals for the cable television system. The combined signals are sent to a transmission module 40 where they are imparted onto the fiber network. In the receiving direction, data from the CPE 14 is received from the fiber network at a receive module 42, sent to a splitter and filter bank 44 and sent to a demodulation circuit DEMOD in the CMTS 30. The data is processed by a network termination unit 46, sent to the switch or router 20 and routed onto the WAN for transmission to the remote computer 10.
Many cable television networks provide only uni-directional cable systems, supporting only a xe2x80x9cdownstreamxe2x80x9d cable data path. A return data path via a telephone network (i.e., a xe2x80x9ctelephony returnxe2x80x9d), such as a public switched telephone network provided by ATandT, GTE, Sprint, MCI and others, is typically used for an xe2x80x9cupstreamxe2x80x9d data path. A cable television system with an upstream connection to a telephony network is called a xe2x80x9cdata-over-cable system with telephony return.xe2x80x9d Such a return system is indicated at 48 where the cable modem 28 is also shown connected to the public switched telephone network (PSTN).
An exemplary data-over-cable system with telephony return includes customer premises equipment (e.g., a customer computer), a cable modem, a cable modem termination system, a cable television network, a public switched telephone network, a telephony remote access concentrator (TRAC 49 in. FIG. 1) and a data network 12 (e.g., the Internet). The cable modem termination system 30 and the telephony remote access concentrator 49 together are called a xe2x80x9ctelephony return termination system.xe2x80x9d
In a two-way cable system without telephony return, the customer premises equipment 14 sends data packets to the cable modem 28, which sends the data packets upstream via the cable television network 22 and 26 to the cable modem termination system 30. Such as system is shown in FIG. 1. The cable modem termination system 30 sends the data packets to appropriate hosts on the data network 12. The cable modem termination system 30 sends the response data packets back to the appropriate cable modem 28.
In a two-way cable system without telephony return, the cable modem termination system 30 can continuously collect information about the level of impairments or other conditions, such as noise floor level, on the upstream RF path of a cable plant, i.e., the portion of the network between the demodulation circuit in the CMTS 30 and the cable modems 28. Further, a single O/E node 24 may serve multiple channels and cable modems. Measurements such as the noise floor level, and signal-to-noise ratio per cable modem transmission, can be made for the coax and fiber networks, along with the tracking of which cable modems are active during a given measurement interval. However, in order for the collected data to be useful, there must be a method of correlating impairments with upstream channels, cable modems, and impairment levels in order for the user (e.g., technician or cable system operator) to ascertain what the cause of the particular impairment is. This problem of correlation is further complicated if there are intermittent, or multiple, impairments on a given upstream path, or across multiple upstream channels.
Unfortunately, the collected impairment data does not lend itself well to plotting on standard format graphs. A tabular presentation of impairment data can involve a significant amount of work by the user to interpret results, and do so in an expeditious manner. Thus, there has been a need in the art for a new method of presenting the impairment data that will allow the user to quickly analyze the data and determine what the cause or causes of the impairments are. The standard way of presenting impairment data or other conditions in a data over cable transmission path is to show the RF spectrum in the channel being monitored with a spectrum analyzer. There are several drawbacks with this approach. First, the method is costly, as in order to get the resolution that is required a separate device is used for data collection. In many cases, the data collection device is limited in how many channels it can monitor. Secondly, the method gives the provider or user no information on active cable modems that may be the cause of the problem. Thirdly, it does not sufficiently narrow down the problem to enable quick troubleshooting of the cause of the impairment. The present invention overcomes these problems.
A method of presenting impairment data in a cable modem system in a useable, easy to understand graphical form is described herein. I have adopted the term xe2x80x9cimpairment circlexe2x80x9d to refer to the graphical representation of the impairment data provided by the method. The impairment circle consists of a circular template, with a line segment superimposed thereon that conveys some information about the impairment or condition being measured. For example, the line segment can represent the magnitude of the impairment or condition being measured. The line segment can also represent the number of occurrences of the impairment during a user defined time period. In another type of impairment circle, the line segment is used to identify cable modems that happen to be active in one or more channels when the impairment is measured, and thus is a tool for isolating which cable modem in which channel is the source of the impairment. Thus, several different types of impairment circles are contemplated.
The perimeter of the impairment circle may be partitioned into a number of small divisions. Depending on the type of impairment circle, the small divisions can represent either individual cable modems, or the number of occurrences of an upstream impairment.
In addition, the impairment circles may have concentric rings centered on the center of the circle, which provide a scale for the line segment superimposed on the circle. For example, the line segment may extend from the perimeter of the circle to the second of three concentric circles, indicating that the magnitude of the impairment that is being measured is equal to the level or magnitude represented by the second concentric circle. The impairment being measured could be conditions such as signal to noise level or noise floor during a period of quiescence in the channel, for example when there are no modems transmitting in the upstream direction during the measurement interval.
In one possible embodiment, an impairment circle is provided which graphically represents impairments across multiple channels on a common upstream path. In this embodiment, the impairment circle is divided into pie-shaped sections. Each section will have the cable modem or occurrence divisions, but they will be for the particular channel that the section represents.
The method, in accordance with a primary aspect of the invention, is a way of presenting impairment data for a data-over-cable system. The method involves, the step of making a measurement of an impairment or condition on a channel of a cable modem transmission path. Then, the measurement is represented as a line segment in an impairment circle having a perimeter and a center. The line segment has a first end on the perimeter of the impairment circle and a second end within the area bounded by the perimeter, and wherein the location of the second end of the line segment within said circle indicates the magnitude of the measurement or impairment.
As an example, the measurement may be made of the signal to noise ratio of a particular upstream channel in the transmission path. The first end of the line segment is on the perimeter of the impairment circle at a location that corresponds to a particular modem in the channel. The second end of the line segment is preferably oriented in a direction towards the center of the circle and terminates at a distance from the perimeter indicative of the magnitude of the signal to noise ratio. The impairment circle provides a very easy to use tool to understand the measurements.
The impairment circles can be used to illustrate, in a convenient and easy to use manner, the effect of an impairment of one channel on separate channels. For example, if a particular modem (e.g., modem no. 3) in channel 1 impairs the active modems in other channels, the impairment circles can illustrate this type of effect.
In this aspect of the invention, a method is provided of presenting impairment data for a data-over-cable system. The method involves generating an impairment circle comprising a circle having a perimeter divided up into a plurality of sections, each section representing a channel in a data-over-cable transmission path and each section having a plurality of divisions, each division representing a cable modem in the channel. Measurements are then made of an impairment in a first channel, with the first channel corresponding to one of the sections of the impairment circle. In the event that the measurement indicates that an impairment exists in the first channel that is affecting one or more of the other channels, a line segment is drawn on the impairment circle. The line segment is drawn between a portion of the perimeter corresponding to the cable modem that is active on the first channel the measurement is made in and a second portion of the perimeter in a second section of said impairment circle corresponding to a second channel. The line segment terminates at a portion of the perimeter in the second section at a region thereof that represents an active cable modem in the second channel.
The impairment circle with the line segment superimposed thereon is generated and presented to the user in a visually perceptible form. For example, impairment circle and line segment could be drawn by a computer and displayed on a terminal or other user interface, printed out on a piece of paper, or even drawn by hand. Preferably, the impairment circles are generated by a software program in a general-purpose computer and displayed on a terminal and printed out on a printer at the option of the user or technician. The software program could either retrieve impairment data from a data base or work in conjunction with another software program that coordinates the actual collection and storage of the impairment measurements.